Field-effect transistor and method of making the same
A semiconductor device includes a semiconductor substrate, a gate structure formed over the semiconductor substrate, and an epitaxial structure formed partially within the semiconductor substrate. A vertically extending portion of the epitaxial structure extends vertically above a top surface of the semiconductor substrate in an area adjacent the gate structure. A laterally extending portion of the epitaxial structure extends laterally at an area below the top surface of the semiconductor substrate in a direction toward an area below the gate structure and beyond an area where the epitaxial structure extends vertically. The device further includes an interlayer dielectric layer between a side surface of the vertically extending portion of the epitaxial structure and a side surface of the gate structure. A top surface of the laterally extending portion of the epitaxial structure directly contacts the interlayer dielectric layer.
1. A method for forming a semiconductor device, comprising:
forming a gate structure over a semiconductor substrate;
forming a capping layer over the semiconductor substrate and the gate structure;
implanting arsenic into the semiconductor substrate, through the capping layer and using the gate structure as a mask, to form an implanted region in the semiconductor substrate;
completely removing the capping layer;
forming an etching spacer on a side surface of the gate structure; and
etching the implanted region, using the gate structure and the etching spacer as a mask, to form a recess in the semiconductor substrate, the recess including an undercut region directly beneath the etching spacer.
2. The method of claim 1 , further comprising:
forming an epitaxial structure in the recess as one of a source or drain region corresponding to the gate structure;
removing the etching spacer; and
forming an interlayer dielectric layer over the epitaxial layer.
3. The method of claim 2 , wherein forming the epitaxial structure includes forming a vertically extending portion of the epitaxial structure extending vertically above a top surface of the semiconductor substrate in an area adjacent the gate structure, and forming a laterally extending portion of the epitaxial structure extending laterally at an area below the top surface of the semiconductor substrate in a direction toward an area below the gate structure and beyond an area where the epitaxial structure extends vertically.
4. The method of claim 3 , wherein forming the interlayer dielectric layer includes forming the interlayer dielectric layer over the laterally extending portion of the epitaxial structure.
5. The method of claim 1 , wherein etching the implanted region to form the recess includes etching the implanted region such that the undercut region of the recess further extends beneath the gate structure.
6. The method of claim 1 , wherein etching the implanted region includes:
performing a dry etching using the gate structure and the etching spacer as a mask; and
performing a wet etching after the dry etching using the gate structure and the etching spacer as a mask.
7. The method of claim 1 , wherein implanting arsenic into the semiconductor substrate includes implanting arsenic at an implantation energy of about 3.5 KeV and an implantation dosage of about 5×10 15 cm −2 .
8. The method of claim 1 , wherein forming the etching spacer includes:
forming a disposable layer over the semiconductor substrate and the gate structure; and
etching back the disposable layer to leave the etching spacer on the side surface of the gate structure.
9. The method of claim 2 , further comprising:
forming a metal contact through the interlayer dielectric layer to contact the epitaxial structure.